Embedding CoMoO4 nanoparticles into porous electrospun carbon nanofibers towards superior lithium storage performance.

CoMoO4 nanoparticles have been successfully in-situ formed and simultaneously embedded within the porous carbon nanofibers (CoMoO4/CNFs) via a facile electrospinning-annealing strategy. The porous CoMoO4/CNFs exhibit a specific surface area of 255.3 m2/g and a pore volume of 0.52 cc/g with average pore diameter of 43.5 nm. The carbon content in the CoMoO4/CNFs can be readily controlled by adjusting the annealing temperature. When examined as anode materials for lithium ion batteries (LIBs), the CoMoO4/CNFs demonstrate superior electrochemical performance, delivering a high reversible capacity of 802 mA h/g after 200 cycles at 200 mA/g and a high-rate capacity of 574 mA h/g at 2000 mA/g. The excellent lithium storage behavior can be attributed to the incorporation of CoMoO4 nanoparticles into the porous N-doped graphitic carbon nanofibers, which efficiently buffer the volume changes of CoMoO4 upon lithiation/delithiation and maintain the overall electrode conductivity/integrity.

Casting amorphorized SnO2/MoO3 hybrid into foam-like carbon nanoflakes towards high-performance pseudocapacitive lithium storage.

We report an amorphorization-hybridization strategy to enhance lithium storage by casting atomically mixed amorphorized SnO2/MoO3 into porous foam-like carbon nanoflakes (denote as SnO2/MoO3@CNFs, or SMC in short), which are simply prepared by annealing tin(II)/molybdenum(IV) 2-ethylhexanoate within CNFs under ambient atmosphere at a low temperature (300 °C). The SnO2/MoO3 loading amount within CNFs can be easily adjusted by controlling the Sn/Mo/C precursors. When examined as lithium ion battery (LIB) anode materials, the amorphorized SnO2/MoO3@CNFs with carbon content of 32 wt% (also denote as SMC-32, in which the number represents the carbon content) deliver a high reversible capacity of 1120.5 mA h/g after 200 cycles at 200 mA/g and then 651.5 mA h/g after another 300 cycles at 2000 mA/g, which is much better than that of the crystalline SnO2/CNFs (carbon content of 34 wt%), MoO3/CNFs (carbon content of 22.7 wt%), or SnO2/MoO3@CNFs (with lower carbon contents of 11 and 25 wt%). The electrochemical measurements as well as the ex situ structure characterization clearly suggest that combination of amorphorization and hybridization of SnO2/MoO3 with CNFs synergistically contributes to the superior lithium storage performance with high pseudocapacitive contribution.

Integrating TiO2/SiO2 into Electrospun Carbon Nanofibers towards Superior Lithium Storage Performance.

In order to overcome the poor electrical conductivity of titania (TiO2) and silica (SiO2) anode materials for lithium ion batteries (LIBs), we herein report a facile preparation of integrated titania⁻silica⁻carbon (TSC) nanofibers via electrospinning and subsequent heat-treatment. Both titania and silica are successfully embedded into the conductive N-doped carbon nanofibers, and they synergistically reinforce the overall strength of the TSC nanofibers after annealing (Note that titania⁻carbon or silica⁻carbon nanofibers cannot be obtained under the same condition). When applied as an anode for LIBs, the TSC nanofiber electrode shows superior cycle stability (502 mAh/g at 100 mA/g after 300 cycles) and high rate capability (572, 518, 421, 334, and 232 mAh/g each after 10 cycles at 100, 200, 500, 1000 and 2000 mA/g, respectively). Our results demonstrate that integration of titania/silica into N-doped carbon nanofibers greatly enhances the electrode conductivity and the overall structural stability of the TSC nanofibers upon repeated lithiation/delithiation cycling.

Construction of three-dimensional ordered porous carbon bulk networks for high performance lithium-sulfur batteries.

In order to suppress the shuttling of soluble lithium polysulfides in Li-S batteries and increase the conductivity of the sulfur cathode, here we report the design and synthesis of three-dimensional (3D) highly ordered porous carbon bulk network (PCBNs), using silica (SiO2) nanospheres as removable hard templates and soluble starch as carbon source. After carbonization and template removal, the as-prepared PCBNs composed of interconnected hollow carbon balls exhibit large surface area (447.4 m2/g) and large pore volume (1.567 cm3/g), high graphitization degree and robust framework. Serving as an efficient sulfur host, PCBNs supported sulfur cathode (S@PCBNs with sulfur content of 72 wt%) delivers a high discharge capacity of 760 mA h/g after 150 cycles at 0.1 C and 455 mA h/g after 400 cycles at 1 C. The superior lithium storage properties is attributed to the novel hierarchical microstructure of the PCBNs, in which the large hollow space not only allows high loading of sulfur but also efficiently accommodates the large volumetric expansion. Moreover, the interconnected PCBNs with high conductivity can spatially confine the shuttling of soluble polysulfides and enhance the redox reaction kinetics.

Chemical vapor deposition growth of carbon nanotube confined nickel sulfides from porous electrospun carbon nanofibers and their superior lithium storage properties.

Multidimensional architecture design is a promising strategy to explore unique physicochemical characteristics by synergistically integrating different structural and compositional materials. Herein, we report the facile synthesis of a novel dendritic hybrid architecture, where carbon nanotubes (CNTs) with nickel sulfide nanoparticles encapsulated inside are epitaxially grown out of the porous electrospun N-doped carbon nanofibers (CNFs) (denoted as CNT@NS@CNFs) through a combined strategy of electrospinning and chemical vapor deposition (CVD). The adopted thiophene (C4H4S) not only serves as a carbon source for the growth of CNTs but also as a sulfur source for the sulfurization of Ni particles and S-doping into carbon matrices. When examined as an anode material for lithium-ion batteries (LIBs), the dendritic CNT@NS@CNFs display superior lithium storage properties including good cycle stability and high rate capability, delivering a high reversible capacity of 630 mA h g-1 at 100 mA g-1 after 200 cycles and 277 mA h g-1 at a high rate of 1000 mA g-1. These outstanding electrochemical properties can be attributed to the novel hybrid architecture, in which the encapsulation of nickel sulfide nanoparticles within the CNT/CNFs not only efficiently buffers the volume changes upon lithiation/delithiation, but also facilitates charge transfer and electrolyte diffusion owing to the highly conductive networks with open frame structures.

Atomic layer deposition of TiO2 shells on MoO3 nanobelts allowing enhanced lithium storage performance.

Atomic layer deposition (ALD) of TiO2 shells on MoO3 nanobelts (denote as TiO2@MoO3) is realized using a home-made ALD system, which allows a controllable hydrolysis reaction of TiCl4-H2O on an atomic scale. When used as an anode material for lithium ion batteries, the TiO2@MoO3 electrode demonstrates much enhanced lithium storage performance including higher specific capacity, better cycling stability and rate capability.

Template synthesis of graphitic hollow carbon nanoballs as supports for SnOx nanoparticles towards enhanced lithium storage performance.

To address the volume change-induced pulverization problem of tin-based anodes, a concept using hollow carbon nanoballs (HCNBs) as buffering supports is herein proposed. HCNBs with hollow interior, flexibility and graphitic crystallization are first prepared by a combined method of chemical vapor deposition (CVD) and template-synthesis using CH4 as the carbon source and CaCO3 as the conformal template. The ultrafine SnO2 nanoparticles are loaded onto the HCNBs (denoted as SnO2@HCNBs) via pyrolysis of tin(ii) 2-ethylhexanoate at 300 °C in air. On further annealing SnO2@HCNBs in Ar, SnO2 is partially reduced to SnOx by consuming a part of carbon of HCNBs as the reducing agent, and thus SnOx@HCNBs are obtained (note that SnOx represents a composite consisting of SnO2, SnO and Sn phases). When applied as anode materials for lithium ion batteries (LIBs), HCNBs deliver high reversible capacities of 841 mA h g-1 after 125 cycles at 200 mA g-1, and 726 mA h g-1 after 400 cycles even at 1000 mA g-1, while SnO2@HCNBs and SnOx@HCNBs exhibit discharge capacities of 1042 and 1299 mA h g-1 after 400 cycles at 200 mA g-1, respectively. Notably, all of them display gradually increased capacity with retention over 100% even after long-term cycling, which is attributed to the novel robust characteristic of the HCNBs as revealed by the ex situ TEM analysis. The flexible hollow HCNBs with high graphitic crystallization not only efficiently tolerate the volume changes of the Li-Sn alloying-dealloying but also facilitate the electrolyte/charge transfer owing to the hollow structure and high conductivity of the HCNBs.

Pyrolytic synthesis of MoO3 nanoplates within foam-like carbon nanoflakes for enhanced lithium ion storage.

MoO3 as electrode material for lithium ion batteries (LIBs) suffers from the poor ionic and electronic conductivity, while hybridizing nanostructured MoO3 with carbon-based materials is regarded as an efficient strategy. Herein, we report the facile synthesis of MoO3 nanoplates within foam-like carbon nanoflakes (CNFs) via the pyrolysis of molybdenum 2-ethtlhexanoate (C48H90MoO12) at a low temperature of 300 °C under ambient atmosphere. Mixing C48H90MoO12 with the highly porous foam-like CNFs allows the sufficient pyrolysis of Mo precursor, which can readily crystallize into MoO3 with plate morphology. The loading amount of MoO3 within CNFs can be easily and precisely controlled by adjusting the relative amount of C48H90MoO12/CNFs, while the plate morphology of MoO3 can be well preserved. The structural characteristics as well as the formation mechanism are investigated. When used as anode material for LIBs, optimized MoO3/CNFs displays superior lithium storage performance, delivering a high discharge capacity of 791 mA h/g after 100 cycles at 500 mA/g and even ∼600 mA h/g at a high rate of 2000 mA/g. Moreover, the present pyrolysis synthetic strategy can be generally applied for low-cost and large-scale fabrication of various MoO3/carbon nanocomposites, which demonstrates great potential in the development of high-performance electrodes for electrochemical energy-storage.